This invention relates to a nuclear reactor having a reactor core and means for determining the flux density in this core and which includes flux detectors located in the core at fixed positions and flux probes which are movable in the core through a range of positions.
The fixed flux detectors are usually used for the control of the reactor, particularly to quickly shut down the reactor in the event excessive flux densities are detected. These fixed detectors are capable of supplying continuous measurement data concerning the core flux density and possibly other values. The number and distribution of these fixed flux detectors are limited by expense.
When the more thorough investigation of the flux densities existing throughout the reactor core is desired, the movable probes are used. For this purpose a relatively large number of tubes extend throughout the reactor core and the movable probes are pneumatically driven into and from the core via these tubes, measurements of the probes after they have left the reactor core permitting the flux density measurements. Because the probes are movable, it is possible to obtain measurements from many more locations in the core than is possible by means of the fixed detectors.
One example of a system using movable probes is the U.S. Weissmann et al. U.S. Pat. No. 3,263,081, dated July 26, 1966. In this patent the probes are spherical pellets. Other forms of such movable probes are available, an example being a tightly coiled helical steel spring of substantial length and having outwardly projecting solid spherical end members, the spring being flexible so it can negotiate turns in tubes, and while in the straight tube portions within the reactor, being a probe of substantial length and which is solid, whereas a string of spherical pellets representing a corresponding probe length, risks lengthwise discontinuities because of possible separation of the pellets from each other.
This spring type of probe is disclosed and claimed by the U.S. Fracke et al. application Ser. No. 277,551 filed Aug. 3, 1972 and issued June 25, 1974 as U.S. Pat. No. 3,819,946.
Although the movable probes provide a more extensive spatial exploration of the flux densities in the reactor core, it has heretofore been usual to put them into operation only according to a definite program, for instance, at intervals of days or fractions of days. The probes are subjected to measurements prior to being introduced into the core, and after they are withdrawn from the core. The result is a discontinuous, intermittent flow of measurement data. However, the results obtained from the more extensive spatial measurements the movable probes make possible, is of particular value in the event of abnormal operating conditions within the reactor core. However, such as in case of danger, such more desirable coverage has not been obtained, unless by accidental coincidence of their programmed operation.